Multi-turn hunting tooth stop



Sept. 8, 1959 w. E. POLLOCK 2,902,876

MULTI-TURN HUNTING TOOTH STOP Filed Dec. 12, 1957 FIG.4

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WIL IAM E. POLLOCK ATTOR NEY United States Patent MULTI-TURN HUNTING TOOTH STOP William E. Pollock, Sun Valley, Calif., assignor to Librascope, Incorporated, Glendale, Calif., a corporation of California Application December '12, 1957, Serial No. 702,361

13 Claims. (Cl. 74-414) This invention relates-to limit stop mechanisms and more particularly to a multi-turn hunting tooth stop mechanism for providing a relatively large integral number of turns between positions of engagement.

The present invention provides an extremely compact and lightweight stop mechanism which is sufiiciently simple in design to afford ease and economy in construction. This invention also provides a relatively large number of complete shaft rotations between its terminal positions and provides a positive stopping action at said terminal positions.

The advantages enumerated above are achieved by the novel design of this stop mechanism which employs the principle of the hunting tooth stop modified to separate the fixed stop abutments by the length of a lead screw. The rotating stop abutments approach the desired terminal positions by differential movement along the lead screw.

An object of the present invention is to provide a hunting tooth stop mechanism operable over a relatively large number of turns.

Another object is to provide a mechanically simple stop mechanism operable over a relatively large number of whole revolutions.

Still another object is to provide an inexpensive rotation limiting device which allows for quick and easy changes of stop limits.

Other and more specific features, objects and advantages of this invention will become further evident from the following description and drawings in which:

Figure l is a longitudinal section of the stop mechanism embodying this invention showing the stop abutments engaged in one terminal position in solid lines and showing the stop abutments engaged in the other terminal position in dotted lines;

Figure 2 is a cross-sectional view taken on the line 22 of Figure 1 showing the stop abutments engaged at one terminal position; v

Figure 3 is a cross-sectional view takenon the line 33 of Figure 1 showing the stop abutments engaged at the terminal position opposite from that shown in Figure 2;

Figure 4 is a schematic view of one embodiment of the present invention.

Referring to Figure 1, a support structure consisting of frame member and an end plate 12 support the stop mechanism. The support structure is journaled to receive bearings 14 and 16 which support a rotatable input shaft 18. The input shaft 18 has a threaded portion cut in the form of a lead screw 20. Splined onto shaft 18 is a gear 22 which engages a mating gear 26 which is rotatably mounted on a fixed shaft 28. Also rotatably mounted on the shaft 28 is an elongated gear 30. The gear 30 meshes with a gear 38 which has a threaded inner portion which is carried by the threaded portion 20 of the input shaft 18 as shown in Figures 1 and 2. The gear ratio between gears 22, 26, 30 and 38 is of critical importance and for a detailed explanation of 'ice this feature of my invention reference is made to the explanation relating to Figure 4. Differential rotation between gears 22 and 38 causes the gear 38 to advance along the lead screw 20. A rotatable stop abutment 40shown in Figures 1 and 2 is mounted on the shaft 28 between the gears 26 and 30 and another rotatable stop abutment 42 is also mounted on the shaft 28 at the other end of the elongated gear 30. The rotatable stop abutment 40 and the gear 26 are held in position by pins 44 and 46 passing through into elongated gear 30. The rotatable stop abutment 42 is held in position by pins 48 and 50 passing into gear 30. Another set of rotatable stop abutments 52 and 54 are attached to the gear 38 by pins 56 and 60 as best shown in Figure 1. In the position shown in Figure 1, the rotatable stop abutment 52 is engaged with the rotatable stop abutment 40 and is shown at one of the limits of rotation of the input shaft 18. This limiting position is also shown in crosssection through the section 22 in Figure 2. The dotted lines in Figure 1 show the movable stop abutment 54 engaged with the rotatable stop abutment 42. This position defines the opposite limit of rotation of the gear 38 on shaft 18, and is further shown in more'detail in Figure 3.

Figure 4 showsa schematic diagram illustrating the tooth ratios between the various gears of the stop mechanism. The gear 22 meshing with a mating gear 26 is shown as an illustration andonly for the purpose of eX-. plaining the relationship of these gears to the, stop mechanism as having the same number of teeth as the gear 26.

The gear 26 may be constructed to have less teeth than the gear 22. In such a. design, a more rapid advance of gear 38 will take place along the lead screw 20 for each revolution of the shaft 18 and the stop will allow fewer turns of the shaft 18 between terminal positions. Thus, the gear- 26, shaft 28 and gear 30 will r0 tate one revolution for each revolution of the input shaft 18. Gear 30 having one .more tooth than gear 26 rotates with gear'26. Thus, the elongated gear 30 rotates one revolution for each revolution of the input shaft 18. The gear 30 has one more tooth than the gear 38.-

Since the gear 38 has one less tooth than its mating gear 30, it rotates one revolution plus one tooth for each revolution of the gear 30. Thus, for one revolution of the input shaft 18the gear 38- rotates one revolution plus approximately onetooth. Since the gear 38 has a differential rotation of one tooth for each revolution of the input shaft 18, it will advance along the lead screw 20 by one tooth for every revolution of the shaft 18. This advance along the shaft 18 of a relatively small part of a revolution along the thread for each turn of the input shaft 18 enables the construction of a device which will advance very slowly into a stopped position.

One further design requirement should be pointed out. During the time in which the gear 38 makes one revolution relative to the gear 30, the gear 38 must advance, along the lead screw 20, a distance sufficient to bring the stop abutment 52 into a position completely clear of stop abutment 40. This will be accomplished when the gear 38 has a differential rotation of one tooth relative to the gear 22 for each revolution of the input shaft 18 if the width of the stop abutment 52 is less than the pitch of a single thread of the lead screw 20. In general, the width of the stop abutment 52 can be made the same number of pitch widths (lead screw 20) as the differential rotation measured in' number of teeth of gear 38 between the gear 38 and the gear 22 for each revolution of the input shaft 18. The same requirement applies to the width of the stop abutment 54.

Some previous stop mechanisms have utilized various other means for differential advance along a lead screw, however, stopping action is obtained by a type of clutchtooth stop: Thus; when a terminalpositionis approached, an engagement of the clutching mechanism insuflicient to hold the shaft is first attained. On successive rotations or me-sharefirmer engagements of the clutehing nreclfanism are maaeuminfinany a complete engagement 'isTeached' and Lhesh aft can rotateno further. Thus the stop; at p'osition's near the 'terinirialpositions offers increased-resistanee'to the turning 'ofthe driving shaftuntil i sufiieient resistance is encountered to holdthe'shaft: is un'd'esirable, sincecompletely free'rotation' up to -the"termina1- position* is most often" desired and i also since the position: of engagementmay depend on the force being supplied toturm the shaft'i This invention 'provides alimit stop-mechanismwhich provides" a positive stopping action at the terminalposition and which allows completely'free rotation of the shaft atallpo'sitions sh'ort of the terminal-position; This results 'frornthe'use of 'th'e hunting'tootlfprinciple; When the movable stop abutment approaches the terminal position; itcomes? into a partially overlappingrelationship with the rotatable" stop abutment However, no "contact can result from this ove'rlappinguntil' the-"stop abutments are'in-th'e properangulanrelationshipsi Thus; according to this invention-,- we reach the" proper angular relationships only after the stop *abutmen'ts are completely overlapping at the position of-"most' positive stopping action.

It should be understood, of course, that the foregoingdisclosure relates to' only apreferred embodiment of'the invention andthat numerous modifications-or alterationsmay be made 'therein without departing 'from'the spirit and thescopeof the invention as set forth in'the ap' pended claims:

I claim:

1: In a stop mechanism for'preventing rotation-beyond desired limits-of a support, a shaft rotatably-mountedon' said'support; a first gear-"carried b'y saidsh'aft, means responsive to rotationofsaid shaft forfeedingsaid first gear progressively alongthe lengthof "said shaft, asecond shaft rotatably mounted on"saidfisupport, a"stub shaft mounted on saidsupportparallel tosa'iddrive shaft', a' first gear carried*by"'said"drive shaft; means'responsive to rotation" of said"drive shaft'for advancing'fsaid first gear progressively alongthe length ofsaid drive shaft,- stop abutments mounted, 'one atea'chsideof said first gear and movabletherewith, a' second gear'mounted on 4. 7. A stop mechanism comprising a support, a drive shaft rotatably mounted on said support, a stub shaft mounted on said support parallel to said drive shaft, a lead screw coaxial with and rotatable by said drive shaft, a first gear threaded upon said lead screw, means responsive to rotation of said drive shaft for advancing said first gear progressively along the length of said lead screw; said means comprising a second gear rotatable by said drive shaft, and a -third gear rotatably mounted on said stub shaftin mesh with said second gear, stop abutments mounted one at each side of said-first gear and movable therewith, a fourth gear disposed about said stub shaft rotatable with said third gear and maintained in mesh with said first gear throughout the progressive advance of said first gear along the length of said lead screw; the gears of one of said pairs having different numbers of teeth, and stop abutments mounted one at each side of said fourth gear and rotatable therewith.

8'. A stop mechanism comprising a' support, a first'shaft rotatably mounted on said support, a second shaft mounted on-said support parallel, to said first shaft, a first gear carried by said first shaft, means responsive to rotation of said first shaft for advancing said-first gear progressively along the length of said first shaft, a stop abutment mounted'on said'first'gear and movable therewith, asecond gear mounted orr said second shaft and maintained in'mesh with said first gear throughout the progressive advance of said'first gear along the length of said first shaft and a stop abutment mounted on said second gear and'rotatable therewith.

9. A stop mechanism according to claim 8 in'which the means responsive torotation of said first shaft for advancing said first gear progressively along the length of said first shaft comprises a third gear mounted on and rotatable with said first'shaft, and a fourth gear rotatably disposed about said second shaft in mesh with said third gear.

10. A' stop mechanism according to claim 8' in which said first and second gears have different numbers of teeth.

11; A- stop mechanism according to claim 9 in which said first and second gears have different numbers of teeth.

12. A'stop mechanism according to claim 9'in which said third and fourth gears have different numbers of teeth.

13. A stop mechanism comprising a support, a first shaft rotatably mounted on said'support, a secondshaft mounted on saidsupport parallel to saidlfirst shaft, a

saidstub "shaft and maintainedilr'mesh withsaid first gear throughout the progressive advance ofsaid" first gear: along the length of said drive. shaft; and "stop abutments mounted,,one=at 'each sid e of said's'econd 'gear a'n'd'rotatable therewith.

3: A stop meclianismmccording'" to claim 2 in which the 'means' responsive" to rotation'of said drive shaft for advancing 's'aid first gear"progressivel3 along the length of' said drive shaft comprises a third". gear mounted on and rotatable"witlfseiiddtiv shaft, and a fourth gear rotatably disposed" about said" stub' shaft in mesh with said third gear.

4; A stop mechanismv according .to-claim. 2 in which said firstv and second gears have different numbers of. teeth.

5. A stop mechanism accordingztolclaim Sin which said-first andsecond: gears have different numbers of teeth.-

6. A stop mechanism according -to'clairn 3- in'whieh said third and fourth gears: have differenti numbers; of teeth.

Iead'screw coaxial'with and rotatable bysaid first shaft, a first gear threaded upon saidlead screw, means responsive'to rotation of said first shaft for advancing said first gear progressively along the length of said lead screw; said means comprising a second gear rotatable by said" first shaft, and a third gear rotatably mounted on. said shaft in mesh with said second gear, a stop abutment'mounted at' one side of said first gear and movable therewith, a fourth gear disposed about said second shaft rotatable with saidthird gear and maintained in mesh with said first gear throughout the progressive advance of said first gear along the length of said lead screw; the gears of one of said pairs having different numbers of teeth, and a stop abutment mountedat one side of said fourth gear and rotatable therewith.

References 'Cited in the file of this patent UNITED STATES PATENTS Rowley et al. June 10, 

